1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device having one or more layers of conductive paths, and more particularly to a method of fabricating a semiconductor device in which a gas, such as air, of low permittivity is trapped in cavities between adjacent conductive paths.
2. Description of the Related Art
Capacitive coupling between mutually adjacent conductive paths in a semiconductor device causes crosstalk and limits the operating speed of the device. A known method of mitigating these problems is to form cavities between the conductive paths and fill the cavities with a low-permittivity material such as air, thereby reducing the capacitive coupling ratio. Conventionally, this is done by covering the conductive paths and the spaces between them with a layer of organic spin-on glass capped by an oxide layer, opening pinholes in the oxide cap layer, removing the spin-on glass through the pinholes by a dry etching process, and sealing the cavities by filling in the pinholes with oxide plugs.
Unfortunately, this conventional process tends to leave an oxide residue inside the cavities. In the worst case, the oxide plugs may fall into the cavities, which then become clogged with oxide debris and with other debris and residue from subsequent fabrication processes. As a result, the cavities are inadequately filled with air, their dielectric characteristics are altered, and the original purpose of forming the cavities is not wholly achieved.
An object of the present invention is to provide a semiconductor device fabrication method that can consistently achieve a desired reduction in the capacitive coupling between adjacent conductive paths.
In the invented method of fabricating a semiconductor device, a plurality of conductive paths, separated by organic spin-on glass, are formed on a semiconductor substrate. Then gaps are formed between the organic spin-on glass and the conductive paths, and the organic spin-on glass is removed through the gaps.
Removal of the spin-on glass through the gaps, which may take the form of fine slits disposed beside the conductive paths, leaves cavities that are substantially free of unwanted residues and debris. The capacitive coupling between adjacent conductive paths is consistently lowered, because the cavities are filled with a low-permittivity material, such as air, which has minimal permittivity.